1. Field of the Invention
The present invention relates to a fuel supply control system of an internal combustion engine for automobiles, more particularly, to a device which is so designed as to calculate fuel supply quantity based on different operating conditions of the engine and to actuate fuel injectors in accordance with the fuel supply quantity.
2. Related Art of the Invention
For use in the fuel supply control system of an internal combustion engine, traditional devices described below are widely known.
In these devices, intake air quantity Q, or intake air pressure PB and engine speed N are detected as engine parameters which relate to the air quantity sucked into cylinders, and based on these parameters the basic fuel injection quantity Tp is computed.
On the other hand, a miscellaneous correcting coefficient COEF based on operating conditions of the engine including engine temperature indicated mainly by the coolant temperature Tw, the air-fuel ratio feedback correction coefficient LMD based on the air-fuel ratio of the intake air mixture which is calculated through the detection of the O.sub.2 concentration of exhaust emission, and the voltage correcting quantity Ts to correct the change in the effective opening time of fuel injectors caused by the battery voltage, are respectively utilized.
The basic fuel injection quantity is corrected by the miscellaneous correcting coefficient COEF, the air-fuel ratio feedback correction coefficient LMD, and the voltage correcting value Ts described above, and the result is set as the final fuel injection quantity Ti (.rarw.Tp.times.COEF.times.LMD+Ts).
In this way, a proper quantity of fuel corresponding to the quantity required by the engine may be supplied by sending to a fuel injector, driving pulse signals with a width equivalent to the final fuel injection quantity Ti, synchronized to the engine revolutions.
The fuel supply quantity Ti is determined, however, to match the engine to provide a steady operating condition. Under these circumstances; the fuel quantity which merges into the wall flow (the fuel adhering to the wall surface of the intake path) and the quantity which is uplifted into cylinders from the existing wall flow turn out to be the same, and an equilibrium state of the wall flow, in which the total quantity of the wall flow would not change, is maintained. Therefore, at the time of acceleration when the wall flow quantity increases, for example, the fuel supply quantity becomes insufficient, thus leading to a leaner air-fuel ration and, as a matter of course, to poorer acceleration performance.
In other words, in a steady operating condition, out of the fuel supplied, the fuel which adheres to the wall surface of an intake path, merging into the wall flow and not supplied directly into the cylinder, and the fuel which evaporates from the wall flow and is sucked into the cylinder, are equally balanced, thus maintaining the wall flow quantity at a certain level corresponding to the engine load, therefore, only by supplying a constant quantity of fuel, it is possible to keep the air-fuel ratio at the target level.
When the engine load is high, however, an equilibrium state is achieved with the greater wall flow quantity, so if the engine is accelerated for example, the fuel newly supplied is used up to supplement this wall flow increase, and the fuel quantity sucked into the cylinders decreases. The equilibrium state recovers again when the wall flow quantity becomes appropriate to the next steady operating condition, so during this transitional operation, the air-fuel ration becomes leaner.
Consequently it is necessary to correct the fuel supply quantity in accordance with changes in the wall flow quantity in order to improve the controllability of the air-fuel ration in transitional operation. However, if there were a change in standing conditions such as an intake valve deposit increase, or a change in fuel properties due to a change in alcohol density in the case of an engine supplied with fuel mixed with alcohol, the initial setting of the wall flow correction would be inappropriate and the controllability of the air-fuel ratio in a transitional condition would deteriorate.
In order to solve the above mentioned problems, the inventor has previously proposed a fuel supply control system which enables learning control of a fuel correcting quantity in transitional operation. (Unexamined Japanese Patent Publication (Kokai) No. 2-61346)
In the conventional transitional learning system, however, air-fuel ratio errors in a transitional condition including various factors such as an air-fuel ratio control error due to the detection response delay of assorted sensors and a change in the required quantity of fuel between the final setting time of the fuel supply quantity and the opening time of intake valves, have been learned instead of the wall flow. Therefore, to learn a fuel correcting quantity in compliance with changes in the wall flow quantity with a high degree of precision, or to grasp the changing condition of the wall flow, has been difficult or impossible.